Special is off 34% from last year's

Despite an all-star lineup that included performances by Mariah Carey, Carrie Underwood, Rihanna, Fergie and the promise of appearances by all three presidential candidates, the show was down 34% among adults 18-49 year-over-year.

Although the two-hour "Gives Back" was Wednesday's highest-rated program (17.6 million viewers and a preliminary 6.7 rating and 18 share), it marks the lowest rating for an "Idol" telecast since 2005's "American Idol's Worst Auditions" special.

By comparison, "Idol" is down only 10% on Wednesdays in general this season.

Fox said that last year's "Gives Back" was advertised as a regular "Idol" result show — viewers who tuned in were surprised to discover that the elimination was pushed to the next episode. This year's episode was considered a special, with no elimination ceremony promised.

Like last year, however, there was a surprise omission: The videotaped messages by Sens. Barack Obama, Hillary Clinton and John McCain were held until Thursday's episode.

The telethon raised $22 million for charity Wednesday, according to Billboard, thanks to a combination of corporate sponsors and viewer donations. Fox said that this year's final tally will be released later and is higher than that amount. Last year, the event raised $76 million.

CBS was second Wednesday with "Big Brother" (6 million, 2.1/6), "Criminal Minds" (13.1 million, 3.3/8) and "CSI: NY" (12.2 million, 3.1/8). ABC was third with repeats and "Supernanny" (5.8 million, 2.2/5). NBC was fourth with "Deal or No Deal" (9.6 million, 2.4/7) and repeats. The CW was fifth with a clip show and "Pussycat Dolls Present: Girlicious" (1.9 million, 0.9/2).